The administrator is required if the software is going toup date the registry - as most good software needs to do.
You can make any user a local administrator of the local NT box - so that they logon onto the network as normal user, but on thier own machine they have admin rights.
Do this by logging onto the local box as adminstrator, then use User Manager in admin tools, go to Adminstrators in bottom half, and add the users domain logon to the local adminstrators.
From then on they will be able to install software locally without needed the admin password.